A known measuring method of the universe of measuring methods for ascertaining fill level in a container is the travel-time measuring method. In the case of this measuring method, microwaves, for example, are transmitted as measuring signals via an antenna apparatus and the echo waves reflected on the surface of the medium detected, wherein the travel time of the measuring signals is a measure for the separation between the antenna apparatus and the surface of the medium. From half the travel time, accordingly, the fill level of the medium in a container can be ascertained. The echo curve represents, in such case, the total course of the signal as a function of time, wherein each measured value of the echo curve corresponds to the amplitude of an echo signal reflected on a surface at a certain distance from the antenna. The travel time measuring method is essentially divided into two methods of ascertainment: in the case of the time-difference measurement, the time, which a broadband wave signal pulse requires for a traveled path, is ascertained. In the case of frequency modulated continuous wave radar (FMCW—Frequency Modulated Continuous Wave), the emitted, frequency modulated, high-frequency signal is compared to the reflected, received, frequency-modulated, high-frequency signal ascertained. In the following, no limitation to a particular method of ascertainment is intended.
For producing frequency—and phase stable signals, which are necessary for coherent methods in communications—and sensor technology, frequently synthesizer circuits are applied, which contain one or more phase control circuits.
In the state of the art are phase control loops with integrated phase control circuits, wherein the phase control circuits have, besides a phase detector, programmable frequency dividers. A part of an output signal of a voltage controlled oscillator is fed back into the phase control circuit and there after passing through a frequency divider compared with a reference signal (in given cases, also frequency divided) in the phase detector of the phase control circuit. The phase detector delivers as output signal of the phase control circuit an electrical current or a voltage, which is proportional to the phase difference between the input signal and the signal of the voltage controlled oscillator. This output signal is fed via a controller to the control input of the voltage controlled oscillator. In the case of correct design of the controller and the factors of the frequency divider, the output signal follows the phase and the frequency of the input signal. Through use of an input signal of high quality, then its good spectral characteristics can be transferred to the output signal. Moreover, the output signal follows frequency- and phase modulations of the input signal.
Sensors of process measurements technology should usually fulfill standards relative to explosion protection, so-called Ex-standards, in order that they can be operated in an environment containing an explosive atmosphere. These Ex-standards are easier to fulfill, the smaller are the maximum needed potential differences and electrical currents and the lower the supply voltages of the circuit components, respectively the circuit groups, and the smaller the number of voltage sources.